As part of SSM’s Initial Review Phase of SKB’s SR-Site safety assessment of the final disposal of spent nuclear fuel at the Forsmark site, Quintessa has been requested by SSM to consider whether SKB’s methodology to abstract FEPs (features, events, processes), as well as site information and other data, into assessment models for radionuclide transport is appropriate and sufficient for its purpose. This Technical Note summarises the findings of Quintessa’s review.
The reviewers consider that SKB’s methodology appears to be appropriate and sufficient but there is scope for improvements to be made in the clarity of its documentation. Information relevant to the radionuclide transport methodology is dispersed around various reports rather than being summarised in a single high level report, which then references supporting detailed reports. The transparency and traceability of the reports is further hindered by the reports rarely providing section numbers when citing other SR-Site reports, and by the preponderance of probabilistic calculations, which makes it much more difficult for the reader to gain a good understanding of what really matters (averaging over a large number of realisations hides important features of the calculations) and hinders the reproduction of SKB’s calculations by a third party.